Cold forming waveguide bending tool

ABSTRACT

A rectangular waveguide bending tool including a forming die containing a waveguide receiving channel bounded along one side by a cylindrically curved forming wall surface and open along its opposite side for singly receiving a waveguide to be bent in an initial position wherein a portion of the guide fits within the channel between its forming wall surface and a stop on the die. A forming block is supported opposite the open side of the channel for relative rotation of the forming die and block about the axis of the forming wall surface with an edge pressure surface of the block in sliding contact with the outer exposed side of the waveguide to bend the waveguide about the forming surface. The pressure surface of the forming block is uniquely contoured to cooperate with the forming die channel in such a way as to bend the waveguide without degradation of its electrical characteristics.

' Unite States Patent 1191 Woodward 1451 Nov. 4, 1975 COLD FORMING WAVEGUIDE BENDING TOOL [57] ABSTRACT A rectangular waveguide bending tool including a forming die containing a waveguide receiving channel bounded along one side by a cylindrically curved forming wall surface and open along its opposite side for singly receiving a waveguide to be bent in an initial position wherein a portion of the guide fits within the channel between its forming wall surface and a stop [52] US. Cl 72/388; 72/459 on the die, A forming block is supported opposite the Ill. (1. pen ide of the hannel for relative rotation of [he Field of Search forming die and block about the aXis of the forming 379 wall surface with an edge pressure surface of the block in sliding contact with the outer exposed side of the [56] References Cited waveguide to bend the waveguide about the forming UNITED STATES PATENTS surface. The pressure surface of the forming block is 268,050 11/1882 Stephens 72/217 to cooperate with the forming F 704,521 7/1902 Dolan 72/310 Channel 111 Such a y as to bend the wavegulde Wlth- 1,133,401 3 1915 Redding 72/217 out degradation of its electrical Characteristics- 3,729,975 5/1973 DelMonica 72/32 R24,646 5/1959 Fuchs 72/l50 Primary Examiner-C. W. Lanham 9 Claims 5 Drawing Figures Assistant ExaminerGene P. Crosby Attorney, Agent, or FirmDaniel T. Anderson; Donald R. Nyhagen; Stephen J. Koundakjian I M l H I I l g: I a lo 64 I 68 7o 32 e2 72 38 Ill ll 1 I r 1 1e T 25 i 1 l nllli- US. Patent Nov. 4, 1975 Sheet 1 of2 3,916,666

US. Patent Nov. 4, 1975 Sheet 2 of2 3,916,666

COLD FORMING WAVEGUIDE BENDING TOOL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to the cold metal working art and more particularly to an improved cold forming waveguide bending tool.

2. Prior Art Microwave construction frequently requires microwave transmission along circuitous paths, thus necessitating wave-guides with corresponding turns or bends. Such nonlinear waveguides may be fabricated in various ways, as by electroforming the guides on appropriately shaped mandrels, which are later removed, constructing the waveguides in appropriately shaped sections which are joined to one another, and physically bending the waveguides. This invention is concerned with this latter fabrication technique.

Broadly speaking, waveguide bending is a highly specialized technique in the more general art of tube and pipe bending. This art is highly developed and replete with a vast assortment of bending tools and machines. Examples of such tools and machines are described in US. Pat. Nos:

US. Pat. Nos. 2,792,048 and Re.24,646 describe a bending tool or machine specifically for waveguides.

As is well known to those versed in the microwave transmission field, waveguides are precision devices which are extremely difficult to bend without degrading their electrical characteristics. For example, even relatively slight changes in the cross-sectional dimensions and/or shape of a waveguide or rippling of the waveguide walls produced by bending generally are sufficient to seriously degrade the waveguide electrical characteristics or totally destroy the usefulness of the guide.

SUMMARY OF THE INVENTION This invention provides an improved cold forming waveguide bending tool whose primary advantage is its ability to bend a rectangular waveguide without significantly degrading its electrical characteristics. Generally stated, the waveguide bending tool has a forming die containing a rectangular channel which is sized to snugly receive the waveguide to be bent. The channel is bounded along one side by a forming wall surface which is cylindrically curved about an axis of the die. The channel is open along its opposite side for receiving the waveguide in an initial position, wherein a portion of the channel fits within the channel between its forming wall surface and a stop on the forming die which engages the waveguide to retain it in the channel.

Located opposite the open side of the forming die channel is a forming block. This forming block has an edge pressure surface facing the channel for sliding contact with the outer exposed side of the waveguide in the channel. The forming die and forming block are mutually supported for relative rotation about the forming die axis with the forming block pressure surface in contact with the waveguide. During this relative rotation, the relative movement of the forming block occurs with a sliding motion along the waveguide to bend the latter around the forming surface and into the channel of the forming die. A close fitting bendable mandrel is preferably inserted through the waveguide to assist in maintaining the internal size and shape of the waveguide during the bending operation. This mandrel is etched away or otherwise removed after the bending operation is completed.

A primary feature of the waveguide bending tool resides in a unique configuration or contour of its waveguide engaging pressure surface. This surface is shaped in such a way that the waveguide is effectively stretched around the forming surface to produce a smooth bend in the guide without altering its internal shape and dimensions and without indenting the guide and hence without degrading its electrical characteris tics. Other features of the bending tool resides in its unique arrangement of parts which facilitates insertion and removal of the waveguide into and from the tool and operation of the tool to produce multiple bends in a waveguide.

In the particular bending tool described, the forming die has an essentially cylindrical configuration, and the forming block is carried by a handle which is removably mounted on the die for rotation of the block and handle about the die. The forming block is adjustable radially relative to the forming die to adjust the radial bending pressure exerted on the waveguide by the block. The forming die is constructed in separate parts which are relatively adjustable for ease of die fabrication, insertion and removal of the waveguide, and multiple bending of the guide.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a waveguide bending tool according to the invention showing the forming die and forming block handle in disassembled relation;

FIG. 2 is a section taken on line 22 in FIG. 1;

FIG. 3 is a view similar to FIG. 2 showing the forming die and forming block handle in assembled relation;

FIG. 4 is a section taken in line 44 in FIG. 3; and

FIG. 5 is an enlarged detail illustrating the waveguide engaging pressure surface of the forming block.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to these drawings, the illustrated waveguide bending tool 10 comprises a forming die 12 having a rectangular waveguide receiving channel 14. Channel 14 curves about an axis 16 of the forming die and is bounded along its radially inner side by a forming wall surface 18 which is cylindrically curved about the axis 16 and along its two adjacent sides by annular wall surfaces 20, 22. These annular wall surfaces extend radially out from the forming surface 18 in planes normal to the forming die axis 16. The channel 14 is open along its radially outer side.

Forming die channel 14 is adapted to receive a rectangular waveguide 24 of substantially the same crosssectional dimensions as the channel in an initial position (FIG. 2) wherein a portion of the guide fits within the channel with the three channel wall surfaces 18, 20 and 22 in seating contact with their adjacent waveguide sides. The remaining side of the waveguide is exposed through the open side of the channel. It will be understood from the foregoing that the forming die channel 14 is sized to receive with a relatively close tolerance fit the particular waveguide to be bent. Mounted on the forming die 12 is a fixed stop 26 for engaging the exposed outer side of the waveguide adjacent the portion of the guide which fits in the channel in the initial waveguide position of FIG. 2.

The bending tool includes in addition to the forming die 12 a forming block 28. This forming block is located in the plane of the forming die channel 14 opposite the open outer side of the channel and has a pressure surface 30 facing the channel for sliding contact with the outer exposed side of the waveguide 24.

Forming die 12 and forming block 28 are connected by means 32 for relative rotation of the die and block about the die axis 16 with the pressure surface 30 of the forming block in sliding contact with the outer surface of the waveguide 24. During the bending operation, the forming die and forming block undergo relative rotation in a manner such that the relative rotation of the block with respect to the die occurs in the direction of the arrow in FIG. 4. In the course of this relative rotation, the forming block undergoes relative movement along the waveguide in a direction away from and from an initial position adjacent the stop 26 and thereby bends the waveguide about the die forming surface 18 and into the forming die channel 14.

As explained below, the forming block pressure surface 30 is uniquely shaped to accomplish this bending operation without degrading the electrical characteristics of the waveguide. A close fitting mandrel 34 is preferably inserted through the waveguide during the bending operation to assist in maintaining the internal waveguide dimensions. This mandrel is made of a material which is bendable with the waveguide and removable from the guide after bending by an acid etching operation or other removal operation.

The particular waveguide bending tool illustrated was actually constructed and used successfully to bend copper waveguides 0.074 in. by 0.148 in. in cross-section to a 0.50 in. radius with an aluminum mandrel inserted through the guide. Referring now in more detail to this illustrated tool, the forming die 12 comprises two separate cylindrical parts 36 and 38. Die part 36 comprises a relatively large cylindrical portion 40, a coaxial smaller diameter portion 42 extending from one end of the die portion 40, and a still smaller diameter stem 44 extending coaxially from the die portion 42. The smaller die portion 42 has a diameter equal to the desired inner radius of the waveguide bend to be formed and its outer surface is the forming surface 18 of the die. The annular shoulder surface formed between the die portions 40, 42 constitutes the annular wall surface of the forming die.

Forming die part 38 has a cap-like shape and includes an upper end wall 46 with a central opening for receiving the die stem 44 and a cylindrical skirt 48 which telescopes over the forming die portion 42 with a relatively close tolerance rotatable fit. The lower end face of the die part or cap 38 constitutes the annular wall surface 22 of the forming die channel 14. Forming die portion 40 and cap 38 have the same diameters, such that their outer cylindrical surfaces are axially aligned and join the channel wall surfaces 30, 22 along the outer edges of these surfaces.

Where the forming die parts 36, 38 are assembled, the end wall 46 of part 38 seats against the annular shoulder 50 formed between the portion 42 and stem 44 of die part 36. This seating engagement of the wall and shoulder locates the die parts relative to one another in the direction of the forming die axis 16 to provide the proper spacing between the forming die channel surfaces 20, 22. The die parts are releasibly held in this assembled relation by a nut 52 threaded on the stem 44 and a spacer or washer 54 between the nut and die part 38.

The waveguide stop 26 comprises a triangular metal bar releasibly secured to the enlarged portion 40 of die part 36 by a bracket 56 bolted to the part. Die part 36 has a number of threaded holes 58 spaced about its circumference to permit the placement of the stop to be adjusted for reasons to be explained shortly. As shown in FIGS. 2 and 4, the stop 26 is positioned with a flat side facing and flush with the open outer side of the forming die channel 14 for contact with the outer side of the waveguide 24. As shown best in FIGS. 1 and 3, the stop extends across the channel, parallel to the die axis 16.

In order to facilitate placement of the waveguide 24 in its initial position of FIG. 2 within the forming die channel 14, the forming die part or cap 38 is formed with a flat 60 in a plane parallel to the die axis 16 and tangent to or preferably intersecting the die forming surface 18. This flat is alignable with the stop 26 by rotation of the cap 38 to its position of FIG. 1 and has a width, axially of the forming die, sufficient to receive the waveguide 24 above the stop 26, in FIG. 1, with the guide seating against the radially inner side of the flat. The waveguide is moved laterally downward in FIG. 1 from this position above the stop to its initial position of FIG. 2 within the forming channel 14, behind the stop. Cap 38 is then rotated from its position of FIG. 1 to its position of FIG. 3 to lock the waveguide in the channel.

As noted earlier, the forming die 12 and forming block 28 are joined by connecting means 32 for relative rotation about the forming die axis 16. In the particular bending tool shown, the connecting means comprises a handle including a handgrip 62 and a sleeve bearing 64 rigid on one end of the handgrip with its axis normal to the axis of the handgrip. Bearing 64 is internally sized to fit rotatably over the forming die cap 38 in the manner shown in FIG. 3. Also rigid on the handgrip is an arm 66 in a plane normal to the axis of the bearing sleeve 64 and spaced along the axis from the bearing sleeve. Arm 66 has a bore for slidably receiving the die stem 44 and forms a thrust bearing engagable with the nut 52 to support the handle 32 axially on the forming die 12 and locate the forming block 28 in the plane of the forming die channel 14.

Forming block 28 comprises a flat plate which seats slidably against a flat surface 68 on'the handle 32 flush with the lower end of the bearing sleeve 64 in FIG. 1. The forming block is rotatably fixed to the adjacent end of a spindle 70 which extends axially through and is threaded within the handle. Fixed to the opposite end of this spindle is a knob 72 by which the spindle may be rotated to move the spindle and thereby the forming block 28 toward and away from the axis of the sleeve bearing 64. The block is prevented from turning with the spindle by engagement of the block with the handle surface 68.

In use of the bending tool as described thus far, the tool handle 32 is removed from the forming die 12 and the forming die cap 38 is rotated to its position of FIG. 1. The waveguide 24 to be bent, along with its internal mandrel 34, is then inserted into the forming die channel, through the flat 60 in the cap, to the initial waveguide position of FIG. 2. Thereafter, the forming die cap is rotated to its position of FIG. 3 and fixedin position by tightening its nut 52 to lock the waveguide in the channel. The handle 32 is now assembled on the forming die 12 by sliding the handle bearing sleeve 64 downwardly over the die cap 38 until the handle thrust bearing 66 engages the nut 52. This engagement of the thrust bearing with the nut locates the forming block 28 in the plane of the forming die channel 14 and hence in position to engage the waveguide 24. When thus assembling the handle of the forming die, the handle is rotated relative to the die to an initial position, shown in broken lines in FIG. 4, wherein the forming block 28 is located as close as possible to the forming die stop 26 and at the trailing side of the stop relative to the direction of rotation of the handle with respect to the forming die.

The waveguide bending operation is then commenced by first rotating the spindle 70 in a direction to advance the forming block 28 against the waveglide 24. The handle 32 is then rotated relative to the forming die 12 in the direction of the arrow in FIG. 1. During this handle rotation, the forming block undergoes movement along the waveguide with the forming block pressure surface 30 in sliding contact with the guide to bend the latter about the die forming surface 18 and into the die channel 14.

As shown in FIG. 5, and described below, the forming block pressure surface is rounded. During sliding movement of the surface along the waveguide 24, the waveguide is closely confined externally by the walls of the forming die channel 14 and the forming block at its region of contact with the guide and internally by the mandrel 34. The forming block exerts a frictional drag on the waveguide, such that the latter is effectively bent or formed about and to the radius of the forming surface 18 with a cold drawing action without altering the internal waveguide dimensions, or indenting, wrinkling, buckling, or otherwise adversely deforming the guide and hence without changing or degrading the electrical characteristics of the guide.

After bending, the waveguide 24 is removed in any convenient way. For example, it may be possible by moving the waveguide endwise from behind the stop 26 and then removing the guide radially from the die channel 14. If necessary, the die cap 38 may be raised above the stop or removed entirely from the die part 36 to permit removal of the waveguide. The stop'itself may be removed from the die, of course, to permit removal of the guide. Also, when making multiple bends in the waveguide, the stop may be adjusted about the forrnng die, as necessary to accommodate the multiple bends.

As noted earlier, the particular bending tool illustrated was actually constructed and utilized successfully to bend copper waveguides with a wall thickness of 0.040 in. and an internal cross-section of 0.074 in. by 0.148 in. to an internal bend radius (forming surface radius) of approximately 0.50 in. without significant degradation of the waveguide electrical characteristics. The pressure surface configuration of the forming block employed in this tool is detailed in FIG. 5.

Referring to the latter figure, the forming block 28 has an edge surface 74 facing the forming die 12 and defined by line elements parallel to the die axis 16. This edge surface includes leading and trailing edge surface portions 76, 78 relative to the direction of rotation of the block with respect. to the die which converge toward the die, a cylindrically curved edge surface portion 80 between the convergent ends of the leading and trailing edge surface portions, and transition edge surface portions 82, 84 between and merging smoothly with the edge surface portions 76, 78, and 80. Edge surface portion 80 is cylindrically curved to a 0.25m. radius about an axis 86 which parallels and is located in a plane 88 containing the axis of the handle bearing sleeve 64 and hence also the forming die axis 16 when the handle 32 is assembled on the forming die 12. This cylindrical surface portion extends through an angle of approximately 25 from the plane 88 toward the leading edge surface portion 76 and from the plane toward the trailing edge surface portion 78 through an angle of approximately 45 The leading and trailing edge surface portions 76, 78 are flat and disposed at angles of approximately 25 and' 45, respectively, relative to a plane 90 which is normal to the plane 88 and hence is tangent to the circular direction line of rotation of the forming block 28 about the forming die 12. The transition edge surface portions 82, 84 merge smoothly with the surface portions 76, 78, and 80 and conform generally to cylindrically curvatures of approximately 0.0625 in. and 0.125 in. radii, respectively. The edge surface portions 80, 82, and 84 together constitute the forming block pressure surface 30. 1

I claim:

1. A rectangular waveguide bending tool comprising:

a forming die having a rectangular waveguide receiving channel curving about the axis of the die and bounded along its radially inner sideby a forming wall surface which is cylindrically curved about said axis and along its two adjacent sides by annular wall surfaces which extend radially out from said forming surface in planes normal to said axis;

said channel being open along its radially outer side for receiving a rectangular waveguide of substantially the same cross-sectional dimensions as said channel in an initial position wherein a portion of the waveguide is positioned in said channel with said channel surfaces in seating contact with three sides of said waveguide portion and the remaining outer side of said waveguide portion is exposed through the open outer side of said channel;

a fixed stop on said forming die for contact with the outer side of the waveguide adjacent said portion thereof for retaining said waveguide portion in said channel;

a forming block located in the plane of said channel opposite the open side thereof and having an edge surface defined by line elements parallel to said forming die axis, said edge surface forming a rounded pressure surface facing said channel for sliding contact with the outer side of the waveguide; and i i means connecting said forming die and forming block for relative rotation about said forming die axis with said pressure surface of the block in sliding contact with the outer side of the waveguide and in a manner such that the relative rotation of said block with respect to said die occurs in a direction away from said stop and along said waveguide from an initial position adjacent said stop for bending the waveguide about said forming surface.

2. A waveguide bending tool according to claim 1 wherein:

7 said forming block edge surface includes convergent leading and trailing edge surface portions relative to said direction of relative rotation of said block which converge toward said forming die and a rounded edge surface portion between and merging smoothly with the convergent ends of said leading and trailing edge surface portions; and said rounded edge surface portion constitutes said forming block pressure surface. 3. A waveguide bending tool according to claim 1 wherein:

said forming block edge surface includes flat convergent leading and trailing edge surface portions relative to said direction of relative rotation of said block which converge toward said forming die, a rounded edge surface portion between the convergent ends of said leading and trailing edge surface portions which is cylindrically curved about an axis of said forming block parallel to said forming die axis and extends from a plane containing said axes toward said leading edge surface portion through an angle of approximately 25 and from said plane toward said trailing edge portion through an angle of approximately 45, and transition edge surface portions between and merging smoothly with said rounded edge surface portion and said leading and trailing edge surface portions; said leading edge surface portion is disposed at an angle of approximately 25 relative to a plane normal to said first mentioned plane and said trailing edge surface portion is disposed at an angle of approximately 45 relative to said normal plane; and said rounded edge surface portion constitutes said forming block pressure surface. 4. A waveguide bending tool according to claim 1 wherein:

said forming die has exterior cylindrical surfaces concentric with said forming die axis and extending axially of the die from said annular channel wall surfaces; and said stop has a waveguide engaging surface flush with said exterior die surfaces and facing said channel. 5. A waveguide bending tool according to claim 4 wherein:

said forming die comprises a first cylindrical part including a first relatively large diameter portion providing one of said exterior die surfaces and one of said annular channel wall surfaces, and a coaxial relatively small diameter portion extending from one end of said large diameter portion and providing said forming surface; said forming die comprises a second cylindrical part rotatable on said small diameter portion of said first die part and providing the other exterior die surface and the other annular channel wall surface; said stop is fixed at one end to one of said forming die parts and extends across said channel to the other die part; and said other die part has a flat parallel to said forming die axis and extending beyond the other end of said stop, and adapted to be aligned with said stop by relative rotation of said die parts to provide a clearance space between said stop and other die part through which the waveguide may be placed in and removed from said channel. 6. A waveguide bending tool according to claim 5 wherein:

said forming die parts are movable axially relative to one another to permit axial separation of said large diameter portion of said first die part and said second die part; and means for releasably retaining said die parts in their normal waveguide bending positions relative to one another. 7. A waveguide bending tool according to claim 6 wherein:

said stop is fixed to said first forming die part; said flat is on said second forming die part; and said connecting means comprises a handle rotatable on said second die part and means mounting said forming block on said handle for adjustment toward and away from said forming die. 8. A waveguide bending tool according to claim 7 wherein:

said forming block edge surface includes convergent leading and trailing edge surface portions relative to said direction of relative rotation of said block which converge toward said forming die and a rounded edge surface portion between and merging smoothly with the convergent ends of said leading and trailing edge surface portions; and said rounded edge surface portion constitutes said forming block pressure surface. 9. A waveguide bending tool according to claim 7 wherein:

said forming block edge surface includes flat convergent leading and trailing edge surface portions relative to said direction of relative rotation of said block which converge toward said forming die, a rounded edge surface portion between the convergent ends of said leading and trailing edge surface portions which is cylindrically curved about an axis of said forming block parallel to said forming die axis and extends from a plane containing said axes toward said leading edge surface portion through an angle of approximately 25 and from said plane toward said trailing edge portion through an angle of approximately 45, and transition edge surface portions between and merging smoothly with said rounded edge surface portion and said leading and trailing edge surface portions; said leading edge surface portion is disposed at an angle of approximately 25 relative to a plane normal to said first mentioned plane and said trailing edge surface portion is disposed at an angle of approximately 45 relative to said normal plane; and said rounded edge surface portion constitutes said forming block pressure surface. 

1. A rectangular waveguide bending tool comprising: a forming die having a rectangular waveguide receiving channel curving about the axis of the die and bounded along its radially inner side by a forming wall surface which is cylindrically curved about said axis and along its two adjacent sides by annular wall surfaces which extend radially out from said forming surface in planes normal to said axis; said channel being open along its radially outer side for receiving a rectangular waveguide of substantially the same cross-sectional dimensions as said channel in an initial position wherein a portion of the waveguide is positioned in said channel with said channel surfaces in seating contact with three sides of said waveguide portion and the remaining outer side of said waveguide portion is exposed through the open outer side of said channel; a fixed stop on said forming die for contact with the outer side of the waveguide adjacent said portion thereof for retaining said waveguide portion in said channel; a forming block located in the plane of said channel opposite the open side thereof and having an edge surface defined by line elements parallel to said forming die axis, said edge surface forming a rounded pressure surface facing said channel for sliding contact with the outer side of the waveguide; and means connecting said forming die and forming block for relative rotation about said forming die axis with said pressure surface of the block in sliding contact with the outer side of the waveguide and in a manner such that the relative rotation of said block with respect to said die occurs in a direction away from said stop and along said waveguide from an initial position adjacent said stop for bending the waveguide about said forming surface.
 2. A waveguide bending tool according to claim 1 wherein: said forming block edge surface includes convergent leading and trailing edge surface portions relative to said direction of relative rotation of said block which converge toward said forming die and a rounded edge surface portion between and merging smoothly with the convergent ends of said leading and trailing edge surface portions; and said rounded edge surface portion constitutes said forming block pressure surface.
 3. A waveguide bending tool according to claim 1 wherein: said forming block edge surface includes flat convergent leading and trailing edge surface portions relative to said direction of relative rotation of said block which converge toward said forming die, a rounded edge surface portion between the convergent ends of said leading and trailing edge surface portions which is cylindrically curved about an axis of said forming block parallel to said forming die axis and extends from a plane containing said axes toward said leading edge surface portion through an angle of approximately 25* and from said plane toward said trailing edge portion through an angle of approximately 45*, and transition edge surface portions between and merging smoothly with said rounded edge surface portion and said leading and trailing edge surface portions; said leading edge surface portion is disposed at an angle of approximately 25* relative to a plane normal to said first mentioned plane and said trailing edge surface portion is disposed at an angle of approximately 45* relative to said normal plane; and said rounded edge surface portion constitutes said forming block pressure surface.
 4. A waveguide bending tool according to claim 1 wherein: said forming die has exterior cylindrical surfaces concentric with said forming die axis and extending axially of the die from said annular channel wall surfaces; and said stop has a waveguide engaging surface flush with said exterior die surfaces and facing said channel.
 5. A waveguide bending tool according to claim 4 wherein: said forming die comprises a first cylindrical part including a first relatively large diameter portion providing one of said exterior die surfaces and one of said annular channel wall surfaces, and a coaxial relatively small diameter portion extending from one end of said large diameter portion and providing said forming surface; said forming die comprises a second cylindrical part rotatable on said small diameter portion of said first die part and providing the other exterior die surface and the other annular channel wall surface; said stop is fixed at one end to one of said forming die parts and extends across said channel to the other die part; and said other die part has a flat parallel to said forming die axis and extending beyond the other end of said stop, and adapted to be aligned with said stop by relative rotation of said die parts to provide a clearance space between said stop and other die part through which the waveguide may be placed in and removed from said channel.
 6. A waveguide bending tool according to claim 5 wherein: said forming die parts are movable axially relative to one another to permit axial separation of said large diameter portion of said first die part and said second die part; and means for releasably retaining said die parts in their normal waveguide bending positions relative to one another.
 7. A waveguide bending tool according to claim 6 wherein: said stop is fixed to said first forming die part; said flat is on said second forming die part; and said connecting means comprises a handle rotatable on said second die part and means mounting said forming block on said handle for adjustment toward and away from said forming die.
 8. A waveguide bending tool according to claim 7 wherein: said forming block edge surface includes convergent leading and trailing edge surface portions relative to said direction of relative rotation of said block which converge toward said forming die and a rounded edge surface portion between and merging smoothly with the convergent ends of said leading and trailing edge surface portions; and said rounded edge surface portion constitutes said forming block pressure surface.
 9. A waveguide bending tool according to claim 7 wherein: said forming block edge surface includes flat convergent leading and trailing edge surface portions relative to said direction of relative rotation of said block which converge toward said forming die, a rounded edge surface portion between the convergent ends of said leading and trailing edge surface portions which is cylindrically curved about an axis of said forming block parallel to said forming die axis and extends from a plane containing said axes toward said leading edge surface portion through an angle of approximately 25* and from said plane toward said trailing edge portion through an angle of approximately 45*, and transition edge surface portions between and merging smoothly with said rounded edge surface portion and said leading and trailing edge surface portions; said leading edge surface portion is disposed at an angle of approximately 25* relative to a plane normal to said first mentioned plane and said trailing edge surface portion is disposed at an angle of approximately 45* relative to said normal plane; and said rounded edge surface portion constitutes said forming block pressure surface. 